1. Field
The present invention relates to offset value correction technologies and, more particularly, to offset value correction devices and offset value correction methods for correcting an offset value in a received signal.
2. Description of the Related Art
In digital communication, a transmitter transmits signal derived by subjecting a symbol to digital modulation. A receiver identifies a symbol in each symbol period by comparing a detected value and a reference symbol value. For generation of a transmitted symbol and detection of a received symbol, a reference value is required. Where Frequency Shift Keying (FSK) is employed for digital modulation, the reference value represents a reference frequency. A shift created between the reference frequency of a transmitter and the reference frequency of a receiver occurs as a Direct Current (DC) offset in a detection signal of the receiver and inhibits symbol detection in the receiver. To cancel a DC offset, a High-Pass Filter (HPF) is used by way of example to filter a DC component (see, for example, patent document 1).
[patent document 1] Japanese Patent Application Laid-open No. 2006-60725
In the case of digital modulation, a detection signal also includes a DC component. Therefore, use of a HPF to cancel a DC offset results in necessary information being lost. Loss of necessary information can cause permanent degradation. The larger the amount of DC offset, the longer it takes to cancel a DC component and the longer it takes to establish synchronization. As a result, it takes longer to receive data successfully.